CD40 signaling rapidly up-regulates CD23b expression before down-regulation of BCL6. (A) Ramos cells were exposed to CD40L for the indicated durations, after which QPCR was performed to detect the mRNA abundance of the CD23b gene product. CD23b mRNA levels were first normalized by GAPDH levels and expressed as fold change compared with untreated cells. (B) BCL6 mRNA levels were detected by QPCR in the same cells as in panel A. Panels A and B correspond to the average of 3 independent replicates. (C) Western blots were performed in cells treated as in panels A and B using antibodies for BCL6 and for actin as a loading control. (D) Densitometry of 3 independent BCL6 Western blot replicates. The signal of each BCL6 Western blot was first normalized by actin levels and then expressed in fold compared with untreated cells. Error bars represent standard error of the mean (SEM).